Current and turbulence characteristics of perforated box-type artificial reefs in a constant water depth

The internal turbulence formed within artificial reefs (ARs) is extremely important. Laboratory experiments were conducted using Particle Image Velocimetry (PIV) to observe the influence of reef configuration on the current and turbulence features of perforated box-type ARs via arranging from one to three blocks, corresponding to the aspect ratio of 1.05, 2.09 and 3.14 respectively. A numerical model with same specifications of the PIV experiment was built and the calculated results were verified using experimental data. Several vortices with different scales and strong turbulence intensity are formed inside and behind the reef. The internal turbulence has been fully developed under the reef configuration with aspect ratio of 2.09. The internal turbulent flow structure was dominated by the horizontal vortex structure, which displayed certain symmetry in the transverse direction because of symmetrical reef structure. The vorticity pattern inside the reefs was dipole-type, regardless of aspect ratio, consisting of two pairs of high-vorticity but opposite rotation direction clouds formed behind the openings of reef stoss face, and symmetrical distribution in both vertical and horizontal direction. This study aims to reveal the reef-induced internal flow structure and fills the gap of existing research.